1. Field
One or more exemplary embodiments relate to an apparatus and a method for calculating a flicker-evaluation value. In particular, exemplary embodiments relate to an apparatus and a method for a flicker-evaluation value which is effective for wide dynamic range (WDR) processing for synthesizing a long exposure image and a short exposure image.
2. Description of the Related Art
A photographing function of the related art, such as a wide dynamic range (WDR) or a high dynamic range (HDR), has been used to continuously capture and synthesize a short-time exposure image (hereinafter, referred to as a short exposure image) and a long-time exposure image (hereinafter, referred to as a long exposure image) in order to acquire an image that captures a dynamic range exceeding a dynamic range which may be captured by a sensor. The photographing function is particularly effective in a condition where contrast, such as a composition of backlight, etc., is very great.
However, two types of problems occur in a structure of the related art which synthesizes the short exposure image and the long exposure image. In the first problem, if a subject moves, an image is distorted when synthesizing images. Thus, a contour is doubled. In the second problem, flicker occurs in the short exposure image. If the short exposure image is used for synthesis, a synthetic image, including flicker, is output. Thus, the synthetic image becomes an image which is difficult to be seen.
A fluorescent lamp having no inverter may cause flicker. Among light-emitting diode (LED) products, there is an LED lamp having a low glimmering frequency. The glimmering of the LED lamp at such a low frequency may be a factor causing flicker. Backlight of a TV system, including a liquid crystal display (LCD) or a PC display, has increasing glimmer so as to improve a moving picture display performance. Glimmering by backlight of a TV system, including a liquid crystal display (LCD) or a PC display, is increased to improve the performance of displaying a moving picture. However, glimmering of the backlight may cause flicker.
A related art technique for reducing flicker of a WDR may be used. For example, there is a related art technique that captures flicker detecting orders of several frames, and determines whether flicker has occurred or determines a frequency according to the capturing result (e.g., see Japanese Patent Publication No. 2012-129972). According to the related art technique, international organization for standardization (ISO) sensitivity or an exposure value (EV) is controlled, or a shutter speed is set to be less affected by flicker, to perform capturing according to the determination result.
There is a related art technique that compares images which are respectively captured at shutter times of 1/240 seconds and 1/60 seconds to detect flicker (e.g., see Japanese Patent Publication No. 2012-119761). In the related art technique, priorities are set with respect to several WDR synthetic images and a gradation correction image of a short exposure image according to the flicker detection result. Further, displaying or recording of the several WDR synthetic images and the gradation correction image of the short exposure image is controlled according to the corresponding priorities.
Further, there is a related art technique which adjusts a difference between white balance (WB) occurring when synthesizing images captured in a flash environment and a WB occurring when synthesizing images captured in a no flash environment (e.g., see Japanese Patent Publication No. 2011-35894). According to the related art technique, average summation is performed on several images to reduce flicker. Also, the average summation is performed on the several images to acquire a WDR effect.
However, Japanese Patent Publication No. 2012-129972 discloses a related art technique which determines whether flicker has occurred or determines a frequency before performing capturing. Therefore, several frames are required for the determination. Thus, the related art technique may not cope with a situation where a flicker light source starts or ends lighting when capturing a moving picture. If a flicker light source having a high luminance is used, information about the high luminance may not be sufficiently acquired.
According to a related art technique disclosed in Japanese Patent Publication No. 2012-119761, if flicker is detected, a priority of a WDR synthetic image is lowered. If the priority of the WDR synthetic image is lowered, e.g., although flicker occurs in a part of a screen, a WDR effect in the whole part of the screen is acquired.
In a related art technique disclosed in Japanese Patent Publication No. 2011-35894, capturing and summation are repeatedly performed until flickers disappear, in order to reduce flickers through average summation performed on several captured images. Also, a plurality of frames are added to acquire a WDR effect, and an effect of extending a range is low.